Method of temporarily closing perforations in the casing



2 Sheets-Sheet l BALLS` mTRooucLo HERE J. V. DERRICK ETAL METHOD 0FTEMPORARILY CLOSING PERFORATIONS 1N THE CASING Filed April 27. 1955 July17, 1956 147/1 l l y BYMM-MMLM lll/11 METHOD OF TEMPORARILY CLOSINGPERFORATIONS IN THE CASING 2 Sheets-Sheet 2 Filed April 27, 1955 TO PUMPSKR R C E 0mm. TRE N E B o 3 www. G EK t M. A uw ,M .J Y O 5 l L a@BALLS INTRODUCED HERE TO PUMP United States Patent C) METHOD FTEMPORARILY CLOSING PERFORA- TIONS 1N THE CASING James V. Derrick andLloyd H. Kaltenberger, Breckenridge, Tex., assignors to The ChemicalProcess Company, Breckenridge, Tex.

Application April 27, 1955, Serial No. 504,212

8 Claims. (Cl. 166-1) This invention relates to oil and gas' welltreating and more in particular to a method of temporarily closingperforations in the casing.

Heretofore it has been a practice in completing the oil and gas wells toset the casing, cement the same and then perforate the casing either byjet or bullet perforations opposite the producing formations. Theseopenings in the well casing are of various sizes depending upon themethod of perforating used.

In completing new oil or gas wells or recompleting old oil or gas wellsit is often necessary to open new drainage channels in the producingformation to provide commercial production. In many cases casing hasbeen set through the formation and the casing is perforated opposite theformation to allow oil or gas to come into the casing from theformation. The well may be treated either by acid treatment or hydraulicfracturing or by numerous other methods embodying the injecting ofiluids or solids into the formation.

The material being injected into the casing and through the perforationsin the casing does not distribute itself equally through all of theperforations and it has been found desirable to close those perforationsthrough which the treating material is moving in order to force thetreating material through other perforations thereby creating newdrainage channels in the producing formation.

Heretofore there have been no known methods of temporarily closing theseperforations selectively during the treating operation. v

It is an object of this invention to close the perforations in thecasing in such a manner that only those perforations are closed throughwhich the fluids forced down the casing are being injected into theformation.

It is also an object of this invention to have these closure meansoperated so that they may be readily removed.

This invention provides a method by which some of the perforations canbe temporarily plugged during an injection of fluids or materials sothat such fluids or materials are forced into the formation throughother perforations which remain open, thus creating several new drainagechannels in the formation.

These and other objects of this invention will become apparent from thepreferred embodiment of the invention which is described hereinafterwith particular reference to the drawings wherein:

Fig. l is a diagrammatic sectional view of a perforated oil Well.

Fig. 2 is a diagrammatic sectional view of an oil well with a packer setnear the end of the tubing.

Fig. 3 is a diagrammatic sectional view of an oil well with the tubingin place.

Fig. 4 is a plan View, partially in section of a coated spherical plug.

Fig. 5 is a plan view in section of a hollow spherical plug.

Fig. 6 is a plan View of a double conical plug.

Fig. 7 is a plan view of a flat plate plug.

Fig. 8 is an edge view of Fig. 7.

In the preferred embodiment of the invention shown in Fig. l, the casing10 is run to the bottom of the well and cemented around the outside, atleast to a distance above the producing strata, as shown. The casing andthe cement 11, are then perforated by any one of various means. If thewell does not immediately come into production it is then commonpractice to treat the well in such a manner as to open up the producingformation to allow a ready passage for the oil to flow into the well.This is accomplished by treating by acidizing, hydraulic fracturing orother methods which comprise forcing a treating material 12 down thecasing 10 and into the producing formation through the perforations 13,13 in the casing. Exceedingly high pressures are sometimes used in thisoperation, in the neighborhood of 10,000 lbs. per square inch, is notunusual, and it is recognized that the material will flow throughcertain of the perforations more readily than it will flow throughothers. It is apparent then that only that part of the formation whichis adjacent to these perforations is being subjected to the treatment.It therefore becomes desirable to close off these perforations duringthe treating operation selectively, that is, those perforations throughwhich the liquid is flowing should be closed so that the liquid will acton the formation adjacent to the other perforations.

In order to accomplish this, balls 14, 14 are introduced into thematerial moving in the casing 10 and are carried by this material downto the point where the material flows through the perforations 13. Theballs are then held by the uid pressure in the casing, which is greaterthan the pressure in the formation, against the perforations in thecasing, thereby effectively closing these perforations until such a timeas the pressure differen` tial is reversed and the pressure in theformation becomes greater or equal to that in the casing, at which timethe balls are forced free of the perforations and drop to the bottom ofthe well and remain there, as shown at 15, 15 in Fig. l. Thispreferential closing of the perforations in the casing allows equaltreatment of the strata through the entire distance of the perforations,for example, the perforations in the lower part may be closed rst, andthen progressively those other perforations carrying most of thetreating material from the casing.

It has been found that plugs having a density greater than the treatingmaterial being injected into the producing formation are mostsatisfactory, so that when the flow is reversed and the plugs fall tothe bottom, due to their greater density, they remain there, but plugsof a density less than the material in the casing may be used and theseplugs will rise with the ow from the well and be removed at the wellhead.

' Where balls have been used in the preferred embodiment of thisinvention other shapes may also be used Y satisfactorily. Solids havingconoidal shapes other than spherical (show-n in Figs. 4 and 5), such aselliptical, or a double conical (shown in Fig. 6) may also be used. Flatplates (shown in Figs. 7 and 8) which will deform to take the curvatureof the casing under the pressures exerted at the bottom of the well alsohave been found to be satisfactory. it is therefore apparent to oneskilled in the art, that plugs of many different shapes may be used.

These plugs must be of such a nature and such a size that they will notgo through the perforations and that they may be readily removed fromthe perforations by the release of pressure in the casing. They must bemade of a material that will not deform to an extent so as to becomepermanently lodged in the perforations. It is necessary in all of thesemodifications that the materials used in making the plugs be of such anature as not to be attacked appreciably by the treating material. Thatis, if hydrochloric acid is being used, aluminum or magnesium plugs arenot satisfactory, as they will be subject to attack by the acid. In thehydraulic fracturing treatment using an oil base to suspend the sand,plugs of magnesium or aluminum alloys can be used. It has been foundmost satisfactory to use an aluminum alloy, steel, bronze, 'laminatedplastic, or hard rubber etc. These plugs may be so-lid or they may beconstructed in two halves so as to form a hollow center (shown in Fig.principally to control the apparent density of the plugs when suspendedin the treating material. The plugs may also be treated on the surfacewith an inert deformable material (shown in Fig. 4) such as neoprenelatex which would act as a gasket when the plugs are brought intocontact with casing perforations. Also hard metal plugs 16 (shown inFig. 4), may be coated with a softer metal 17 which would deform underextreme pressure experienced in the casing to assist in plugging theperforation.

Plugs may be introduced into the bottom of the well suspended on a wireline and attached thereto by an easily broken means. The uid may then bepumped down the casing and when it is desired to close off theperforations opposite the more ,permeable part of the formation, thewire line is raised allowing the plugs to be carried by the uid streamagainst the perforations in the casing and thereby effectively closingthe same. They are held in place as pointed out above by lthe differencein pressure inside and outside the casing.

The well in addition to the casing may have therein a string of openended tubing 18 terminating in the neighborhood of the perforated area,as shown in Figs. 2 and 3 and may have a packer 19 sealing off theannulus between the tubing and the casing above the perforations asshown in Fig. 2. The treating material 12 is pumped down the tubing andilows through the perforations into the adjacent formation. The plugsare admitted through the lubricator 20 and are allowed to move down thetubing 18 with the treating material where they are forced selectivelyagainst those perforations 13 through which the treating material ismoving as shown at 21, leaving open those perforations through which thetreating material is not being injected. These plugs seal off the saidperforations just so long as the pressure within the tubing and thecasing is greater than the pressure in the formation. When the pressureis released at the top of the tubing the plugs will be released from theperforations andthe ow will be established.

The method shown in Figs. 1, 2 and 3, all represent modifications ofthis invention, which comprises basically the introduction of plugs intoa casing during treatment of the producing formation to selectivelyclose the perforations in the casing, closing off those perforationsthrough which the treating `material is most rapidly 'being injected.The invention is not limited by he type of plug but comprises basicallythe selective closing of -such `perforatio-ns. This closing is `of natemporary nature yand only is maintained vduring the injecting of thetreating material into the permeable formation, and when the pressure isreleased the plugs are self-acting and drop clear of the perforations soas to allow flow from the producing zone or formation. The methods shownin Figs. l, 2 and 3 are all similar insofar as the plugs are pumped downthe well with the treating material into the general proximity of theperforations in the casing and seal olf those perforations through whichthe material is being injected most rapidly into the adjacent formation.The plugs are carried by the uid stream to the particular perforationthrough which the treating material is entering the formation and thesealing action can be determined readily by the increase in pressure atthe well head. The plugs can be admitted or introduced as desired andmove readily with the material traveling at a rate such that it can beeasily determined when they will arrive at the sealing position and theplugs can be admitted one or two or as many at a time as neededaccording to the pressure rise and fall within the casing. During thepumping of treating material the pressure will constantly rise untilsuch time as the material is injected into the formation. It will thenprobably drop, indicating that the formation has broken and at this timeplugs will be introduced into the fluid stream to plug the perforationsopposite the existing permeability.When this occurs the pressure willagain rise, indicating that the pressure is being exerted againstanother part ofthe formation where little or no permeability exists.When this part at the formation breaks, the pressure may again drop, atwhich time more plugs will be admitted to plug those perforations-through which iiuid is now moving. This procedure can be followed untilas many formation breaks are obtained as desired, or until all of theperforations are plugged. This allows, for the first time, control ofthe fluid entry into the formation of a treating material by the sealingoff of perforations adjacent to the more permeable part of the producingformation.

Heretofore the only means of plugging the perforations in the casingconsisted of a cementing operation which -was of a permanent nature. Thesealing means introduced by the method disclosed herein is of such anature that it can be readily removed without expense or withoutintroducing any undesirable materials into the permeable formation.

While certain arrangements and specific details have been set forth inthis specification to illustrate the invention it is clear that oneskilled in the art may vary the specific details without departing fromthe spirit of the invention which is only limited by the claims attachedhereto, wherein:

What is claimed is:

l. A method of temporarily plugging the perforations in a casing whichhas been set in a bore hole, which comprises: injecting a tiuid underpressure into the casing to cause a ilow of iiuid through thoseperforations which are adjacent portions of a formation in which Ktheback pressure is less than the pressure of the stream, adding pluggingelements which are larger than the perforations in the casing to thestream while maintaining the pressure on the stream whereby certain ofthe plugs will be caused by the flow of iiuid to lodge against saidperforations through which the liquid has been passing and seal thesame.

2. A method of treating a formation in which a casing has been set andperforated, the formation having such characteristics that a liquid willpass through only certain of the lperforations into the formation totreat the formations opposite said perforations, which comprises:introducing into the well a formation treating material containingplugging elements which are larger than the perforations and which willseat themselves only against the above mentioned certain perforationsthrough which the treating material is passing to essentially seal saidperforations in the'casing and cause said stream of treating materialyto pass through other perforations which have not been sealed off, byraising the pressure on said Stream until said treating fluid has beenforced through all of the perforations. v

3. A method as claimed in claim 2, wherein said plugging elements arespherical.

4. A method as claimed in claim 2, wherein said plugging elements arespherical and formed of a hard material having a thin coating of softermaterial on the surface thereof.

5. A method as claimed in claim 2, wherein said plugging elements aremade from a light metal alloy.

6. A method as claimed in claim 2, wherein said plugging elements arehollow steel balls.

7. A method as claimed in claim 2, wherein said plugging elements aremade from a plastic substance selected from the group consisting ofthermo-plastic and thermosetting resins. g

8. A method as claimed in claim 2, wherein said ele= ments are polygonalin shape and insoluble in the treating material.

References Cited in the file of this patent UNITED STATES PATENTS2,699,212 Dismukes Ian. 11, 1955

1. A METHOD OF TEMPORARILY PLUGGING THE PERFORATIONS IN A CASING WHICHHAS BEEN SET IN A BORE HOLE, WHICH COMPRISES INJECTING A FLUID UNDERPRESSURE INTO A CASING TO CAUSE A FLOW OF FLUID THROUGH THOSEPERFORATIONS WHICH ARE ADJACENT PORTIONS OF A FORMATION IN WHICH THEBACK PRESSURE IS LESS THAN THE PRESSURE OF THE STREAM, ADDING PLUGGINGELEMENTS WHICH ARE LARGER THAN THE PERFORMATIONS IN THE CASING TO THESTREAM WHILE MAINTAINING THE PRESSURE ON THE STREAM WHEREBY CERTAIN OFTHE PLUGS WILL BE CAUSED BY THE FLOW OF FLUID TO LODGE AGAINST SAIDPERFORMATIONS THROUGH WHICH THE LIQUID HAS BEEN PASSING AND SEAL THESAME.